The present invention relates to an automatic station searcher for a receiver, and particularly relates to a receiver in which data on broadcasting stations whose received electric field intensities are higher are stored with priority in a presetting storage section.
A tuner capable of preset tuning is known having an automatic station search function wherein frequency sweeping such as scanning is carried out. The sweeping is temporarily stopped when a sufficiently strong signal is found, the frequency of the received signal is stored in a storage section, and sweeping is then resumed to find other signals. However, it is likely that in an urban area or the like where the electric field intensities of received broadcasting stations are relatively high, the number of received broadcasting stations will exceed the capacity of the presetting storage section before the end of the automatic station search operation. Hence, some broadcasting stations at higher frequencies, for example, may not be preset in the storage section.
An automatic station search system has been proposed in which data concerning received broadcasting stations having higher electric fields intensities are stored with priority in a presetting storage section, thus eliminating the above-mentioned drawback. Such a system is disclosed in Japanese Unexamined Published Patent Application No. 186821/82. Such a conventional automatic station search system will hereafter be described with reference to FIG. 1.
Referring to FIG. 1 a superheterodyne receiver includes an antenna 1, a front end (radio frequency stage) 2, an intermediate frequency stage 3, a detector stage 4, an audio amplifier 13, and a phase-locked loop 5. The frequency division ratio of the phase-locked loop 5 can be set by a control section 9 to receive a station of a desired frequency. The output from the intermediate frequency stage 3 is converted into a DC level (SL) by a level detector circuit 6. The DC level is compared with a reference voltage by a level comparator circuit 7. When the DC level is higher than the reference voltage, the DC level is converted into a digital value (DSL) by an A/D converter 8. The digital value is applied to the control section 9.
A storage section 11 is connected to the control section 9. Data M.sub.1 -M.sub.n (such as frequency information) 11b and the digital values (DSL) 11a (such as signal strength values) for a prescribed number of received stations are stored in the storage section 11. The control section 9 regulates the writing and reading of the data into and from the storage section 11.
Presetting keys P.sub.1 -P.sub.n correspond to the data M.sub.1 -M.sub.n stored in the storage Section 11. One of the preset keys P.sub.1 -P.sub.n is operated to send a control signal from the control section 9 to the phase-locked loop 5 on the basis of the frequency information of the corresponding data to receive the broadcasting station of the specified frequency.
When a station search command section 10 commands the control section 9 to start an automatic station search operation, the control section issues a sweep command to the phase-locked loop 5. As a result, the phase-locked loop 5 performs sequential sweeping within the specified frequency band. The received signal from the output of the intermediate frequency stage 3 is converted to a DC level (SL) by the level detector 6. The DC level is compared with the reference voltage. When the DC level is higher than the reference voltage, the DC level is converted into the digital value (DSL) by the A/D converter 8. The DC level is then stored together with the frequency information at a prescribed position in the storage section 11. The seqential sweeping operation is then continued to repeat such operation.
Digital value (DSL) already stored in the storage section 11 corresponding to received stations and newly generated digital values corresponding to stations currently being received are compared with each other and the DC levels are sequentially stored in the order of the magnitudes of the corresponding digital values.
If the received frequency band contains frequencies of broadcasting stations as shown in FIG. 1, the DC levels for the stations are ranked in the order of G, B, A, F and C, although the digital values for the stations should be 5, 4, 3, 2 and 1, for instance. That is, the order of the data of received station information stored in the storage section 11 through such an operation corresponds to that of the intensities of the electric field strength of the received stations.
Another conventional automatic station search system, one in which data on received stations having higher intensities of electric fields are stored with priority similarly to the above conventional automatic station search system but in the order of the frequencies of the stations, has been disclosed in Japanese Unexamined Published Patent Application No. 212819/82.
Although the data on the preset received stations are stored in the order of the electric field strengths or in the order of the frequencies thereof in the conventional automatic station search systems described above, there is a disadvantage in that the user cannot preset the received stations in an optional order. Since the data on the preset received stations are not arranged in relation to the frequencies in the system in which the data are stored in the order of the electric field strengths, there is a practical inconvenience in that the user cannot know which preset button the broadcasting station he wants to receive corresponds to.